Starting the other day I noticed a vibe at about 55 mph, seems to not be there at lower speeds, or higher speeds, above 60 mph.

I have changed the front brake pads a few weeks ago, was out of town, and just got back last week...I thought the pads wore quickly, but they were some NAPA hybrid pads, so i figured maybe that is why.

Any ideas?

If this occurred after you installed the brake pads that's what caused the vibration. Chances are your rotors need to be turned, since the new pads are always in contact with them that's where the vibration comes from.
Gary

Thanks Gary, I will say the vibe didn't start right after I installed pads though, it has taken a week or so.

Well I am going to have the front rotors turned...I went and removed the rear tires to check it out back there...just like with the front, there is one side that the pads are worn down a lot more than on the other side..again, some hybrid NAPA brake pads. With the front it was the right side, with the rear its the left side.

My tires have good tread and I keep them at 35psi, but both rear tires are worn weird on the inside portion...almost cupping. The outside tread and center are fine and the inside isn't worn, just a mild case of cupping.

Not sure what is going on to cause this stuff.

If you still have that vibe after doing this, you might have bad u-joints on the drive shaft. The needle bearings flatten out and induce a harmonic vibe at certain speeds. Down side if that is the problem is that the u-joints can't be replaced by themselves. The entire shaft has to be replaced.